The nervous system and the mapping of the neurons in the gastropod Helix lucorum L.]

Summarized literature and experimental author's data are presented concerning the structure of the nervous system and identification of individual neurons in the snail Helix lucorum. Information about especially well-known neurons is given in a table, maps of the ganglia are presented altogether with the results of retrograde staining of different cerebral and suboesophageal nerves. Are given the references concerning morphology of the central nervous system of the snail and identifiable neurons.     

The potential role of CO2 in initiation and maintenance of estivation in the land snail Helix lucorum

Elevated CO(2) levels are hypothesized to play a role in the initiation and maintenance of estivation in snails through disturbances of acid-base status. The aim of our study was to identify the ambient CO(2) threshold that induces disturbances in acid-base status in the air-breathing land snail Helix lucorum. Acid-base parameters were determined in the hemolymph of snails acclimated to 0.5%, 1%, 2%, 4%, and 8% CO(2) in air for 20 d. In addition, we evaluated the effects of long-term acclimation on metabolic rate and on levels of D-lactate dehydrogenase activity (D-LDH) and of D-lactate in snails after 20 d of exposure to increased CO(2) levels. Helix lucorum proved to be unable to compensate for a decrease in extracellular pH (pH(e)) when acclimated to levels higher than 1% CO(2) in air. The rate of oxygen consumption started to decrease when snails were acclimated to 0.5% CO(2) in air. However, there was no correlation between the drops in pH(e) and in metabolic rate. Long-term acclimation to elevated CO(2) levels induced an increase in the activity of D-LDH with a concomitant accumulation of D-lactate in tissues. This indicates that long-term acclimation to elevated ambient CO(2) levels could reduce the aerobic capacity of land snails and trigger expression of anaerobic pathways of ATP turnover. The threshold levels of ambient CO(2) that induce changes in acid-base status and elicit metabolic depression in adult land snails H. lucorum are higher than the future atmospheric levels that are expected to result from human use of fossil energy resources.     

Synapses identifiable in the parietal ganglia of the snail Helix lucorum

The synaptic plasticity is a background for learning and memory. Identifiable synapses that are the synapses between individually identifiable neurons are a very convenient model for studying plasticity. Synapses between the interoceptive mechanosensory neurons and the command neurons of the withdrawal behavior were identified in the Helix lucorum brain. It was shown that synaptic plasticity estimated by the dynamics of the elementary postsynaptic potentials elicited by single presynaptic spikes differed from the synaptic plasticity estimated by the dynamics of compound synaptic responses of the same neurons to sensory stimulation. Habituation and heterosynaptic facilitation phenomena are discussed in terms of the dynamics of the elementary postsynaptic potentials.     

Diurnal rhythms in cyclic nucleotide metabolism in Helix nervous system.

Concentrations of cAMP (cyclic adenosine 3',5'-monophosphate) and cGMP (cyclic guanosine 3',5'-monophosphate), in ganglia from the garden snail Helix pomatia, vary considerably over the course of the day. There is a maximum in the concentration of both cyclic nucleotides between 08:00 and 12:00 (lights on 06:00 to 18:00), with the cAMP maximum occurring slightly later than that in cGMP. In addition there can be several smaller maxima in cAMP and cGMP levels; the timing of these can be markedly different from experiment to experiment, with cAMP and cGMP sometimes in and sometimes out of phase with each other. This pattern is observed in Helix which had been activated from the dormant state 4-6 days earlier, but is not present in dormant or in long-active animals. The cyclic nucleotide rhythm can be seen in ganglia maintained in organ culture, and persists for at least 24 hours after removal of the tissue from the animal. There appears to be little change in the level of basal or NaF-stimulated adenylate cyclase activity in Helix ganglia over the course of the day. On the other hand, both cAMP and cGMP phosphodiesterase activities exhibit rhythms which are consistent with the rhythms in cAMP and cGMP concentrations.     

Cellular reactions to elaboration of a backward conditioned connection in Helix lucorum

After 10-15 food stimuli paired with electrical shock in semi-intact snail preparation, responses to strong tactile stimuli identified feeding behaviour neurones were studied. Inhibition evoked by tactile stimulation in these cells before learning procedure disappeared and in some cases noxious stimulus evoked synaptic activation corresponding to feeding reactions in the intact animal. Changes in second-order sensory neurones pre-synaptic to the command neurones of avoidance behaviour are suggested to be the mechanism of forward conditioned connection as well as the mechanism of backward conditioned connection.     

NPY- and C-PON-immunoreactive substances in the central nervous system of Helix pomatia

The distribution of neuropeptide-tyrosin (NPY)- and C-flanking peptide of neuropeptide-tyrosine (C-PON)-immunoreactivities in the central nervous system of the pulmonate gastropod, Helix pomatia, was investigated. NPY- and C-PON-like substances were localized in neuronal somata and neuntes, but were not co-localized within the same cells. NPY-immunoreactive substances were also found in endocrine/paracrine like cells located in the epineurium. C-PON and NPY, both reduced serotonin activated isometric contractions of Helix aorta, suggesting that they may act as modulators in the control of the vascular system.     

Nocistatin: a novel neuropeptide encoded by the gene for the nociceptin/orphanin FQ precursor

We identified a novel neuropeptide and named it "nocistatin." Its presence was expected by analysis of the precursor for the neuropeptide nociceptin or orphanin FQ (Noc/OFQ), previously identified as an endogenous ligand for the orphan opioid receptor-like receptor. The precursor prepronociceptin/orphanin FQ (ppNoc/OFQ) comprises at least two bioactive peptides, nocistatin and Noc/OFQ. Noc/OFQ is involved in a broad range of pharmacological actions in various tissues from the central nervous system to the periphery. In pain transmission, Noc/OFQ is reported to have different effects including nociception, no effect, and analgesia, depending on the animal species tested, doses, route of administration, and so on. We found that intrathecal administration of Noc/OFQ induced pain responses including allodynia and hyperalgesia. Simultaneous administration of nocistatin blocked the allodynia and hyperalgesia induced by Noc/OFQ, whereas anti-nocistatin antibody decreased the threshold for the Noc/OFQ-induced allodynia. The endogenous heptadecapeptide nocistatin was isolated from bovine brains and recently identified in mouse, rat, and human brain and in human cerebrospinal fluid. Although human, rat and mouse ppNoc/OFQ produced larger respective counterparts with 30, 35, and 41 amino acid residues, all peptides showed the antinociceptive activity. This activity was ascribed to the carboxyl-terminal hexapeptide of nocistatin, Glu-Gln-Lys-Gln-Leu-Gln, which is conserved beyond species. Nocistatin also attenuated the allodynia and hyperalgesia evoked by prostaglandin E(2) and the inflammatory hyperalgesia induced by formalin or carrageenan/kaolin, and reversed the Noc/OFQ-induced inhibition of morphine analgesia at picogram doses. Furthermore, nocistatin counteracted the impairment of learning and memory induced by Noc/OFQ or scopolamine. Nocistatin is widely present in the spinal cord and brain. Although nocistatin did not bind to the Noc/OFQ receptor, it bound to the membrane of mouse brain and spinal cord with a high affinity. Nocistatin is a novel bioactive peptide produced from the same precursor as Noc/OFQ, and it plays important roles in the regulation of pain transmission and learning and memory processes in the central nervous system.     

Immunocytochemical Study of the Distribution of hcs2 Gene Products in Command Neurons of the Helix lucorum Snail

The distribution of the putative protein products of gene hcs2 in giant command neurons of the parietal ganglia of the terrestrial snail Helix lucorum has been studied using light- and electron-microscopic immunocytochemistry. The product of the hcs2 gene is a hybrid protein belonging to the EF-hand family of Ca²⁺-binding proteins and is a precursor of several neuropeptides. Polyclonal antibodies to neuropeptides CNP3 and CNP4 and the C-terminal Ca²⁺-binding domain of the precursor protein have been used to determine their intracellular localization. The targets for all three types of antibodies have been found in cytoplasmic secretory granules. The label (colloidal gold) density in the secretory granules is two times higher in the case of neuropeptides CNP3 and CNP4 than in the case of the Ca²⁺-binding domain. Thus, a specific association between the putative products of the hcs2 gene and the cell secretory apparatus has been demonstrated. This agrees with the earlier hypothesis that hcs2 products may serve as neurotransmitters or neuromodulators.     

NO-Dependent Regulation by Glutamate of Activity of the Serotoninergic System of the Edible Snail Helix lucorum

This work is a continuation of the study on transmitter regulation of the serotoninergic system activity in the brain of the edible snail Helix lucorum, in which serotonin and NO donors have been shown to excite serotoninergic neurons from various snail ganglia (more than 60 of them were studied) and synchronize their activity by activation of the synchronous synaptic inputs. In the current work, it has been shown that glutamate, on the contrary, has an inhibitory and desynchronizing action on the same serotonin-containing neurons by suppressing their own activity and switching off the synchronous synaptic inputs. In the same neurons, another glutamate receptor agonist, NMDA, has a pronounced excitatory effect and activates the synchronous synaptic inputs. The glutamate effects are NO-dependent: the NO donor sodium nitroprusside decreases, switches off entirely, or transforms the glutamate inhibitory effect into the excitatory one. A possible mechanism of interaction of serotonin, glutamate, and NO in regulation of the snail serotoninergic system activity is discussed.     

Elementary and compound postsynaptic potentials in the defensive command neurons of Helix lucorum

The present communication concerns with the analysis of elementary and the compound excitatory postsynaptic potentials (eEPSPs and cEPSPs) recorded by intracellular microelectrode from an identified defensive command neuron of the snail Helix lucorum. The eEPSPs were evoked by single presynaptic action potentials (APs) elicited by cationic current injection into one of the identified sensory neurons synapsing on the respective command neuron. The cEPSPs were elicited by local brief tactile stimuli on the skin or internal organs. It was shown that the cEPSPs amplitudes depend mainly on the number of activated sensory neurons. Compound EPSPs depend also on frequency and the number of APs in the bursts occurring in a single neuron. Presynaptic APs having frequency 2-10 Hz evoke high frequency depression of that eEPSPs after an interval is followed by post-tetanic potentiation of single eEPSPs. Preceding stimulation of a pneumostom area facilitates the cEPSPs elicited by repeated stimulation of viscera. The eEPSPs from the same visceral area demonstrate no heterosynaptic facilitation in experiments with double parallel intracellular recording from responsive sensory and command neurons. The different types of the eEPSPs plasticity are discussed according to their contribution cEPSPs plastic changes.     

Ca-dependent regulation by Na, K-pump of post-tetanic sensitization of extrasynaptic choline receptors in Helix lucorum neurons

Posttetanic potentiation (by orthodromic stimulation) of cholinosensitivity in LPa3 and RPa3 Helix lucorum neurons that are command in respect to withdrawal behavior was shown earlier (Pivovarov et al., 1999). Now we studied the regulatory role of the Na,K-pump and intracellular free Ga2+ in the posttetanic potentiation (PTP) of cholinosensitivity in command neurons. Semiintact Helix preparation "CNS-visceral bag" was used in experiments. Acetylcholine-induced inward currents were recorded using two-electrode voltage clamp technique. Acetylcholine was applied to somata of the identified LPa3 and RPa3 neurons with a 10-min interval before and after electrical tetanic stimulation of the n. intestinalis (10.5 mA; 0.1 s; 2/s; 2 min). Ouabain (extracellular application, 70 mcM) blocked the PTP. Intracellular injection of BAPTA (1 mM), chelator of Ca2+ ions, prevented the PTP. The PTP was absent after the ouabain application against the background of preliminary intracellular injection of BAPTA. A conclusion war drawn about Ca-dependent participation of Na,K-pump in posttetanic potentiation of cholinosensitivity in command Helix lucorum neurons of withdrawal behavior.     

Noggin基因与中枢神经系统发育的研究进展

Noggin作为一种重要的胚胎蛋白,在胚胎背腹轴模式形成、神经管发育及神经诱导方面有重要功能。干细胞研究的新进展提示,中枢神经系统发育将持续至生后及成年,包括胚胎及成体干细胞的增殖与分化,而noggin通过拮抗骨形成蛋白（BMPs）参与胚胎及成体干细胞的增殖与分化。本文就noggin基因在中枢神经系统发育中的重要功能予以阐述。     

绿盲蝽中枢神经系统的解剖结构

【目的】阐述绿盲蝽Apolygus lucorum中枢神经系统的组成,辨识各组成部分的神经节解剖结构及其形态,计算中枢神经系统各神经节结构体积大小、解析其空间分布关系以及连接模式。【方法】采用免疫组织化学方法,使用突触蛋白抗体对绿盲蝽中枢神经系统神经髓进行染色标记,利用共聚焦激光扫描显微镜获取中枢神经系统各结构数码图像,使用三维图像分析软件对绿盲蝽中枢神经系统进行分析,并构建三维模型。【结果】绿盲蝽中枢神经系统从前往后分别由脑神经节、咽下神经节、前胸神经节和后部神经节组成。脑、咽下神经节和前胸神经节3个神经节融合在一块,形成脑-咽下神经节-前胸神经节复合体,并通过长的神经连索与后部神经节相连,从外观上看似由2个大的神经节构成,这种神经节愈合形式尚未在昆虫中发现过。前胸神经节与后部神经节分离,二者由长的神经连索连接起来。除前胸神经节由单独的神经原节构成外,其他3个神经节又由多个神经原节融合而成。脑包括前脑、中脑和后脑3部分。咽下神经节包括上颚神经节、下颚神经节和下唇神经节。后部神经节包括中胸、后胸和腹部神经节3部分。【结论】明确了绿盲蝽中枢神经系统的神经节构成,发现了绿盲蝽中枢神经系统各神经节的高度融合特性。该项研究结果为研究绿盲蝽中枢神经系统的发育、重塑和系统演化奠定了形态学基础,为研究中枢神经元形态、分布以及其对昆虫生理和行为的功能调控机制提供了结构框架。     

Functional roles of microglia in the central nervous system

Microglia, a type of perineuronal glial cells in the central nervous system, have been suggested to play various important roles in normal and pathologic brains. In this article, first, we described the association or roles of activated microglia in injury and various brain diseases, and subsequently, summarized microglia-derived physiologically active molecules which will affect the neuronal survival and neuronal growth, and glial function, and finally, discussed the molecular mechanism of microglial activation.     

A novel neuropeptide precursor gene is expressed in the terrestrial snail central nervous system by a group of neurons that control mating behavior

We report the isolation of a cDNA clone encoding a neuropeptide precursor named preproGFAD from the central nervous system (CNS) of the snail Helix lucorum. Analysis of the expression of this gene shows that it is neurospecific and expressed in several groups of CNS neurons. Most notable is the expression of preproGFAD gene in the right mesocerebrum, where the neurons controlling mating behavior are located. The expression in this particular region is observed in adult animals but not in juvenile ones. The preprohormone is 108 amino acids long and contains a hydrophobic leader peptide and eight Lys-Arg recognition sites for endoproteolysis. The post-translational processing of the prohormone may lead to the generation of seven tetrapeptides, Gly-Phe-Ala-Asp-COOH (GFAD). This peptide has the same sequence as two previously isolated peptides from a related snail, Achatina fulica. The first of them (achatin-I) contains D-Phe; the second (achatin-II) is its L-Phe-containing stereoisomer. Injection of synthetic D-GFAD in nanomolar concentrations into intact animals caused an increase of the heartbeat rate and opening of the genital atrium. In preparations containing CNS with intact innervation of reproductive organs, bath application of D-GFAD caused extensive movements of the penis but not of other reproductive organs. Intracellular activation of individual neurons expressing the preproGFAD gene also elicited penis movements. D-GFAD also suppressed activity of neurons modulating feeding behavior. Our data therefore indicate that the preproGFAD gene encodes the precursor of a neuropeptide that participates in the regulation of male mating behavior. © 1998 John Wiley & Sons, Inc. J Neurobiol 35: 183–197, 1998     

Functional regulation of GABAA receptors in nervous system pathologies

Inhibitory neurotransmission is primarily governed by γ-aminobutyric acid (GABA) type A receptors (GABAARs). GABAARs are heteropentameric ligand-gated channels formed by the combination of 19 possible subunits. GABAAR subunits are subject to multiple types of regulation, impacting the localization, properties, and function of assembled receptors. GABAARs mediate both phasic (synaptic) and tonic (extrasynaptic) inhibition. While the regulatory mechanisms governing synaptic receptors have begun to be defined, little is known about the regulation of extrasynaptic receptors. We examine the contributions of GABAARs to the pathogenesis of neurodevelopmental disorders, schizophrenia, depression, epilepsy, and stroke, with particular focus on extrasynaptic GABAARs. We suggest that extrasynaptic GABAARs are attractive targets for the treatment of these disorders, and that research should be focused on delineating the mechanisms that regulate extrasynaptic GABAARs, promoting new therapeutic approaches.